The present invention relates to a method and an apparatus for controlling the idling speed of an internal combustion engine.
A well-known method for controlling the speed of an engine when the throttle valve is at the idling position consists of providing an air-control valve in an air bypass passage, which is connected in parallel with the intake passage of the internal combustion engine in order to by-pass the throttle valve in the intake passage, and adjusting the air-control valve to control the flow rate of the air that passes through the air bypass passage. In this closed loop type method of control, the air-control valve is adjusted to control the flow rate of the intake air in accordance with the difference between the desired idling speed of the engine and the actual idling speed of the engine so as to bring the actual idling speed close to the disired idling speed.
The conventional art, however, did not take into consideration atmospheric pressure in controlling the flow rate of the intake air. When an engine according to the conventional art is operated at high altitudes, therefore, its air-control valve does not adjust the actual idling speed as much as it should due to the reduced density of the intake air. When the amount of load applied to the engine by the air-conditioner, power-assisted steering, and/or transmission gear is further changed under such conditions, the actual idling speed of the engine deviates even more from the desired value, in the worst case, causing the engine to stall.